This invention relates to loudspeaker systems, and more particularly to a loudspeaker system in which a plurality of loudspeaker units are employed to provide a desired directivity pattern.
A loudspeaker system is known in the art, in which a plurality of loudspeakers are used to provide a desired directivity so that sound is transmitted only in a desired direction and no sound is transmitted towards a microphone which is the sound source, so as to prevent howling (or acoustic feedback). One example of the loudspeaker system of this type is a so-called Tonesaulen type loudspeaker system in which, as shown in FIG. 1, a plurality of loudspeaker units 1 through 6 are arranged in a single speaker assembly, all of the speakers having an equal diameter. As used herein, the term "speaker assembly" refers to a plurality of loudspeakers in a single enclosure or, if in separate enclosures, disposed immediately adjacent one another so that the listener cannot discern any "separation" and the speaker assembly will appear to the listener as a single sound source. If, in the case where these loudspeaker units 1 through 6 are point sound sources and are arranged on a straight line at equal intervals d as shown in FIG. 2, the angle measured from the perpendicular bisector Z of the X-axis is represented by .UPSILON., then the directivity factor D is represented by the following expression (1): ##EQU1## where k=.omega./c, .omega. is the angular frequency, and c is the sound propagation velocity.
FIG. 3 shows the directivity patterns in the case of kd=0.5, kd=2 and kd=8. In the case of kd=8, the directivity pattern is very sharp, but the directivity pattern unfortunately changes with frequency.